In a typical cellular radio system, also referred to as a wireless communication system, User Equipments (UEs) communicate via a Radio Access Network (RAN) to one or more core networks. The user equipments may also be known as mobile terminals and/or wireless terminals. In particular, the user equipments may be mobile stations or user equipment units, such as mobile telephones (e.g., “cellular” telephones), and laptops with wireless capability (e.g., mobile termination). User equipments may therefore be portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with the radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “eNB”, “NodeB” or “B node” and which in this document is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. The base stations communicate over the air interface, operating on radio frequencies, with user equipment units that are within range of the base stations.
In wireless communication systems, the radio UpLink (UL) is the transmission path from the user equipment to a base station and the radio DownLink (DL) is the transmission path from a base station to the user equipment. In Release 8, of the 3GPP Long Term Evolution (LTE) standard, the arrival of new UL data of higher priority than the already existing data, or of any priority when there is no previous data, to the UE buffer triggers a so-called Regular Buffer Status Report (BSR). There are, of course, side conditions to this. For example, new UL data only triggers a BSR if it is data for a logical channel belonging to a Logical Channel Group (LCG). Further, the “arrival of new UL data” is defined as when UL data becomes available for transmission in a Radio Link Controller (RLC) entity, or in the Packet Data Convergence Protocol (PDCP) entity. The PDCP is an upper layer of the RLC entity
However, notwithstanding these side conditions, the arrival of new UL data generally triggers a regular BSR. The regular BSR, in turn, triggers the generation of a Scheduling Request (SR) trigger. The SR trigger then triggers an SR to be conveyed to the base station, thereby informing the base station that the user equipment has new data that it would like to transmit. The SR is transmitted to the base station either on (1) the user equipment's preallocated scheduling request resource on a Physical Uplink Control Channel (PUCCH), in which case the SR is known as dedicated SR (D-SR) since it is transmitted on a resource dedicated to the user equipment, or (2) on the Physical Random Access Channel (PRACH), in which case the SR is known as a random access SR (RA-SR). In both cases, there is a fixed periodicity associated with the opportunities to transmit an SR. This means that, in order to transmit an SR, the user equipment has to wait until such an opportunity is available.
When the base station receives a D-SR, the base station typically issues an UL grant. When the user equipment transmits on that grant, it will transmit a MAC Packet Data Unit (PDU) that includes a BSR in the shape of a so-called BSR Medium Access Control (MAC) control element, describing the size of its buffers. The BSR is mandated to reflect the buffer status after the MAC PDU, including the BSR MAC control element, is built. A BSR is always included if a BSR trigger is pending in the user equipment at the time of building the MAC PDU, unless all data can fit in the MAC PDU but there is not room enough for a BSR in addition to the data.
Once the size of the user equipment buffer has been reported to the base station, there is no need for the user equipment to send additional SRs as the base station now knows how much data the user equipment has to transmit. The SR trigger can hence be cancelled in the user equipment, so that the user equipment will not send any D-SR at the next D-SR opportunity.
Please note that in the description below, the following terminology will be used:
The term “arrival of new data” is used to indicate arrival of new UL data in the user equipment buffer, with all side conditions for triggering a Regular BSR satisfied.
The term “reception of grant” is used to indicate the reception of a Physical Downlink Control Channel (PDCCH) grant for Uplink Shared Channel (UL-SCH) resources for a new transmission.
The term “transmission of data” is used to indicate transmission of UL data on UL-SCH resources that have been made available for a new transmission.
The term “SR” and “scheduling request” is used to indicate signalling of D-SR on the PUCCH.
The term “SR trigger” and “scheduling request trigger” is used to indicate a pending SR.
When expressions such as “buffer status report accounts for first data” are used, it means that the buffer status report reflects whatever is left of the first data after the transmission in which the buffer status report is included has been received.
An SR is considered pending until cancelled, i.e. an SR trigger that triggers the transmission of an SR, is considered pending until cancelled. It was first agree upon, in a prior version of the LTE standard, that an SR would be cancelled in the first possible Transmission Time Interval (TTI), also known as subframe, when UL-SCH resources for a new transmission are granted. However, some argued that it was unclear exactly when UL-SCH resources for a new transmission are granted, whether it be when a PDCCH grant is received or in the TTI when the UL-SCH resources are actually available. It was subsequently agreed upon that all pending SRs should be cancelled in the TTI when UL-SCH resources are actually available for a new transmission.